In general, natural gas (NG) is a fossil fuel which consists primarily of methane and is buried underground in a gaseous state. Unlike other energy sources such as petroleum (gasoline, diesel) that are subjected to artificial processing, the natural gas is gas energy that can be used immediately after directly collected from a gas well.
These days, with the rise of oil price, gas resources such as coalbed methane and shale gas are attracting attention. Especially, the coalbed methane extracted from coalbed is highly favored as a new-generation energy resource in many countries.
As a technique to upgrade the quality of this natural gas, there are known an absorption method of separating methane and carbon dioxide by using a difference in their solubility, a PSA (Pressure Swing Adsorption) method of separating gas-phase substances by using a difference in their adsorption characteristics, a membrane separation method using a difference in permeability of gas molecules, and so forth.
The absorption method accompanies large energy consumption and involves high cost for maintenance such as replenishment of an absorbent or the like, whereas this method features high separation/refinement efficiency and thus can be mainly used for the processing of a large quantity of gas. The PSA method lies between the absorption method and the membrane separation method in the aspect of separation/refinement efficiency, scale and complexity of the process. The membrane separation method is conducted on a relatively smaller scale than the absorption method or the PSA method, and it is difficult to achieve high-purity methane with this method. Nevertheless, the membrane separation method has an advantage in that the process is simple.
Meanwhile, since the composition of a gas drilled and produced from a gas well could be changed with the lapse of time, a process of separating and refining the produced gas is required to be designed as being capable of eliminating and separating impurities stably while overcoming the change in the composition of the gas.
To this end, there has been a demand for a system capable of obtaining a product gas having high purity and high recovery rate by eliminating and separating impurities continually and stably even if the composition of the natural gas produced from the gas well changes.
Patent Document 1: Korean Patent No. KR 10-0753207 (Registered on Aug. 28, 2007)